It's the intersections of the A4 and Hoe Benham Lane, just under halfway from Newbury to Hungerford on the A4. If you're looking on Google maps, it's at the point labelled "Halfway", because it's half way along the route from London to Bristol.
The pub is under the spot marked B, in
this link.
I would encourage people coming from the Bristol, Bath and Swindon to take the A4